Induction cooking hob

ABSTRACT

An induction cooking heater including an inductor having a number of magnetic field concentration bars located beneath the inductor. The inductor having the magnetic field concentration bars is supported by a polymeric frame. The polymeric frame includes a first support element on which the inductor is wound and a second support element that supports the magnetic field concentration bars. The first support element and the second support element are assembled together through a central ring-shaped zone having a snap engagement. The inductor is wound on an upper surface of the first support element opposite to the second support element.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/153,901 filed May 13, 2016, entitled INDUCTION COOKING HOB,which claims priority to European Patent Application No. EP 15167775.4,filed May 14, 2015, entitled INDUCTION COOKING HOB, the entiredisclosures of which are incorporated herein by reference in theirentirety.

FIELD OF DISCLOSURE

The present disclosure relates to an induction cooking heater of thetype comprising at least one inductor and magnetic field concentrationbars located beneath the inductor, the inductor and the magneticconcentration bars being placed on a polymeric frame, such framecomprising a first support element on which the inductor is wound and asecond support element which supports said magnetic field concentrationbars, both said elements being assembled together.

BACKGROUND

It is well known in the art of induction cooking appliances thatinductors, i.e. induction coils, present a strong part to part variationespecially in a not entirely automatic process of manufacturing thesecomponents (i.e. a process entirely carried out by robots or the like),particularly when the coil pancake elements are joined together using aglue which is also used to fix not only inductor and ferrites, but alsomineral wool, mica and aluminum tray.

This aspect significantly influences the cooktop performances and thedesign development, and therefore the production process stronglyaffects the inductor quality. For the above reasons many applianceproducers now use a plastic frame structure that increases theuniformity of products because it fixes the routing of the coil windingturns and the relative position between ferrites and wire.

A great number of producers adopt a solution in which induction coilsare mounted on a plastic frame which is used for the coil winding on oneside and for placing the ferrite bars on the other side. There are alsosolutions with a plastic frame is used only for ferrite bars while thewinding is placed over with glue or bi-adhesive stripes.

The above known solutions have the disadvantage of making the productionprocess quite complex and difficult to carry out in a totally automaticway. Moreover, the different temperatures reached by the magnetic fieldconcentration bars and coil lead the designer to choose a polymericmaterial which can withstand the highest temperatures and therefore thepolymeric support needs to be made of a quite expensive polymer whichcan withstand such high temperatures.

The technical solution of the induction cooking heater disclosed byCN201414236 has the disadvantage of increasing the distance between thewindings of the inductor and the ceramic glass where a cooking utensilis placed. This is due to the thickness of the first plastic frame whichis interposed between the windings and the glass of the cookingappliance. Such an increased distance decreases the energy efficiency ofthe inductor. Moreover, since the windings of the inductor on the firstplastic frame is usually performed so that the wire is placed on theframe from above, it is necessary to flip over the upper frame duringthe assembly process of the two frames, and this leads to a complicationof the assembly line.

Another disadvantage of the above known solution derives from the almostidentical diameters of the two plastic elements which are connected ontheir peripheral edge, since this requires a large amount of polymericmaterial.

It is an object of the present disclosure to provide an inductioncooking heater which does not present the problems detailed above.

BRIEF SUMMARY

According to one aspect of the present disclosure, an induction cookingheater is provided. The induction cooking heater includes an inductorhaving a number of magnetic field concentration bars located beneath theinductor. The inductor having the magnetic field concentration bars issupported by a polymeric frame. The polymeric frame includes a firstsupport element on which the inductor is wound and a second supportelement that supports the magnetic field concentration bars. The firstsupport element and the second support element are assembled togetherthrough a central ring-shaped zone having a snap engagement. Theinductor is wound on an upper surface of the first support elementopposite to the second support element.

According to another aspect of the present disclosure, an inductioncooking heater is provided. The induction cooking heater includes aninductor having a number of magnetic field concentration bars locatedbeneath the inductor. The inductor having the magnetic fieldconcentration bars is supported by a polymeric frame. The polymericframe includes a first support element on which the inductor is woundand a second support element that supports the magnetic fieldconcentration bars. The first support element and the second supportelement are assembled together through an annular zone having a snapengagement. The inductor is wound on an upper surface of the firstsupport element opposite to the second support element. The firstelement presents a plurality of arms stemming out from a central zonethat are joined at an intermediate ring.

According to yet another aspect of the present disclosure, a method forproducing an induction cooking heater is provided. The method forproducing the induction cooking heater includes at least one inductorand a group of magnetic field concentration bars located beneath theinductor, the inductor and the group of magnetic field concentrationsbars are supported by a polymeric frame. The method for producing theinduction cooking heater further includes winding a wire on an uppersurface of a first support element opposite to the field concentrationbars, inserting said magnetic field concentration bars on a secondsupport element, and assembling together the first support element andthe second support element.

These and other features, advantages, and objects of the present devicewill be further understood and appreciated by those skilled in the artupon studying the following specification, claims, and appendeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the present disclosure will becomeclear from the following detailed description, with reference to theattached drawings, in which:

FIG. 1 is a partial cross section view of an induction cooking heateraccording to a first embodiment of the present disclosure where someancillary components (connection wires, insulation layers etc.) havebeen omitted for sake of clarity;

FIG. 2 is similar to FIG. 1 and relates to a second embodiment of thedisclosure;

FIG. 3 is a top view of the lower plastic support element used in theinduction cooking heater of FIG. 2;

FIG. 4 is a top view of the upper plastic support element used incombination with the lower plastic support element of FIG. 3;

FIGS. 5-7 are different versions of the lower plastic support elementwhich can be combined with upper elements;

FIGS. 8-10 are different versions of the upper element which can becombined with any of the lower elements of FIGS. 5-7;

FIGS. 11-12 are top views of the lower support element of FIG. 3 withferrite bars of different lengths mounted thereon;

FIGS. 13-14 are similar to FIGS. 11-12 and show the lower supportelement of FIGS. 6 and 7 with ferrites mounted thereon; and

FIGS. 15-16 are top views of further embodiments of the upper plasticsupport element designed to increase mechanical robustness of theinductor plastic frame.

DETAILED DESCRIPTION OF EMBODIMENTS

For purposes of description herein the terms “upper,” “lower,” “right,”“left,” “rear,” “front,” “vertical,” “horizontal,” and derivativesthereof shall relate to the device as oriented in FIG. 1. However, it isto be understood that the device may assume various alternativeorientations and step sequences, except where expressly specified to thecontrary. It is also to be understood that the specific devices andprocesses illustrated in the attached drawings, and described in thefollowing specification are simply exemplary embodiments of theinventive concepts defined in the appended claims. Hence, specificdimensions and other physical characteristics relating to theembodiments disclosed herein are not to be considered as limiting,unless the claims expressly state otherwise.

According to the disclosure, the double frame is created with two joinedelements, a first or upper support element 12 and a second or lowersupport element 14. The upper support element 12 for coil winding andthe lower support element 14 for the ferrite bars, does not increase thedistance of the coil windings from the ceramic glass, thereforeincreasing the efficiency of the inductor.

According to a preferred feature of the disclosure, the second supportelement 14 of the frame presents a dimension sensibly lower than thedimension of the first support element 12, therefore allowing areduction of the amount of polymer material needed for the plasticframe. Preferably the first and second elements are made of differentpolymeric materials, and they are preferably assembled by means of snapengagement portions placed in the inner zone of said elements and/or inan intermediate zone comprised between the center ring-shaped zone andthe peripheral edge or outside peripheral ring.

According to the claimed features of the disclosure it is possible toobtain an energy efficient, flexible and a cheaper solution compared toprior art that can be produced with a high efficiency line automationprocess characterized by an high productivity.

With reference to the drawings and particularly to FIG. 1, an inductioncooking heater 10 comprises an upper plastic support element 12comprising a plurality of radial arms 12 a stemming out from a secondcentral ring-shaped zone 12 b (only half of this central zone is shownin FIGS. 1 and 2). On an upper surface 11 of the upper support element12 provided with a plurality of grooves G, a wire W is wound. Below theupper support element 12, a lower plastic support element 14 is placed,which in the embodiments shown in FIGS. 3, 5, 6 and 7 presents a firstcentral ring-shaped zone 14 a.

The assembly between the upper support element 12 and the lower supportelement 14 is carried out in their respective central zones where pins16 provided in the upper elements 12 cooperate with correspondingcentral seats 18 provided in the lower elements 14. This solution allowsfor a greater number of wound wires in the central area of the inductorthus increasing the probability to detect a pot with a lower bottomdimension. Snap engagement means (not shown) assure a quick and stableconnection between the two elements, even if a manual disassemblythereof is not prevented. The number of pins 16 (four in the shownexample) and of the corresponding matching central seats 18 assure acorrect positioning of the upper and lower support elements 12 and 14.

According to FIG. 3, an embodiment is shown in which the coupling of theupper support element 12 and the lower support element 14 is carried outby protruding pins 21 in the lower support element 14 which are matchingcorresponding seats 27 of the upper support element 12 provided in anannular intermediate ring 15 thereof. Of course the fastening orcoupling solutions of the above two embodiments can be combined togetheras well.

Magnetic field concentration bars 20 or ferrite bars 20 are entrappedbetween the first support element 12 and second support element 14, andtherefore glue or bi-adhesive are no longer necessary (with a decreaseof overall cost). In order to assure a fixed position of the ferritebars 20, the lower support element 14 presents preferably seats 22(shown in FIG. 3 as radial tile-shaped portions stemming out from anannular portion 14 b placed at a predetermined radial distance from thering-shaped) whose dimensions match the dimensions and shape of theferrite bars 20. Between the first central ring-shaped zone 14 a and theannular portion 14 b an intermediate zone 14 c is defined with shapedseats S for additional ferrites.

According to the solution shown in FIG. 5, the lower support element 14does not need to have a lower wall, rather it can have only a side wall24 for centering the ferrite bars 20 on an auxiliary support plateplaced below the inductor (not shown).

Moreover, the shape of the lower support element can vary from the onesshown in FIGS. 3 and 5 and it can have several arms (FIG. 6) stemmingfrom the first central ring-shaped zone 14 a and connected to an outsideperipheral ring 26. In such embodiment the first central ring-shapedzone 14 a presents a radial lowered area 25 which is radially alignedwith corresponding lowered zones 28 in said peripheral ring 26 forcontaining ferrite bars 20.

The seats in the lower support element 14, for each type of lowersupport element 14 shown in FIG. 3, 5, 6 or 7 present a radial end 23near to the first central ring-shaped zone 14 a of the lower supportelement 14 while the other side is open so as to allow the insertion offerrite bars 20 which extend over and exceed the axial dimension of theseats 22, as clearly shown in FIGS. 12 and 14. For avoiding anaccidental sliding of the ferrite bars 20, the upper support element 12presents, for each of its arm 12 a, a L shaped portion 13 (FIGS. 1 and2) which acts as a radial stop for the ferrite bars 20. It is importantto notice that the dimensions of the lower support element 14 can bereduced at minimum because the larger extension is done only by theferrite length (FIGS. 12 and 14). So for each coil size and for eachgroup, a ferrite placed in the plastic frame support 14 can be joinedwith a greater coil winding to the upper support element 12 thatcorresponds to the coil's nominal size. The first central ring-shapedzone 14 a of the lower support element 14 may be also used for insertingauxiliary ferrites 30 having a circular shape, particularly a circularsector shape (FIGS. 11-13). Such solution has the advantage of higherstandardization (the internal ferrites structure of a coil can be equalfor all the coil round shape dimensions because the inductor size can beobtained using different lengths of the ferrite bars 20), thermalefficiency (the winding internal section of a coil is the hottest partand a larger ferrite layer under this zone permits to reducetemperatures), and higher cooking performances (the presence of theferrites in a zone nearer to the coil center permits to reach a betterheating uniformity on the pot bottom and a lower influence on thetemperature sensor of the winding magnetic flux lines).

In a way similar to the lower support element 14, the upper supportelement 12 can also have different shapes and three additional variantsare shown in FIGS. 8-10. Of course the shape will be chosen also inrelation to the numbers and dimensions of the coil wires, allowing thedesigner to easily combine different elements in order to obtain thebest result either in terms of mechanical strength and confinement ofthe magnetic field.

According to another embodiment (FIG. 15), the arms 12 a of the uppersupport elements 12 present an outer reinforcing ring 40. In theembodiment of FIGS. 9 and 16, the number of arms 12 a outside theintermediate ring 15 and referred to in the drawings with reference A,is identical to the number of arms 12 a inside the ring 15, identifiedin the drawings with reference B, but with an angular offset. In FIG. 6such arms A and B are in a radial distribution with reference to theintermediate ring 15. In the embodiment of FIG. 10, the number ofoutside arms A is double the number of inner arms B. The Applicant hasdiscovered that both solutions according to FIGS. 9, 16, and/or 10present a very low warping after injection moulding process, and thisresult is obtained with a very low amount of polymer used for the frame.

The snap joint solution permits having at the same time a windingstructure with the desired number of arms (useful to improve mechanicalrobustness of the support) and a suitable ferrite quantity in view ofthe central and/or intermediate joint between such elements. Inparticular a winding plastic frame can be joined with a different armnumber ferrite plastic support using the external ring 40 in order toavoid the accidental sliding of the ferrite bars.

According to another preferred feature of the disclosure, an overallcost saving is possible by using different plastic materials for the twosupport elements on the basis of the maximum temperatures reached.Usually the ferrite bars 20 arrive at temperatures (around 140° C.) thatare lower if compared with the temperatures of the windings (200°C.-220° C.). Therefore for the lower support element 14 a lowerperformance polymeric compound can be used, for instance a thermoplasticpolymer chosen from polyamides (nylon 6,6), polyolefins, polystyrene andrelated polymers, polyvinlylchloride and related polymers and saturatedpolyesters. For the upper support element 12 a heat resistant polymer ispreferred, for instance polyphenylene sulfide (PPS) reinforced withglass fibers. Of course other engineering polymer can be used.

Another substantial advantage of the induction cooking heater accordingto the present disclosure relates to the induction coil automation lineprocess improvement. The number of line steps can be reduced compared toknown solutions since the plastic support flip over phase is no longernecessary. The main result is that coil wire wrapping and ferritesinsertion steps can be done in parallel, reducing in this way the piececycle time. So, by increasing the pieces number per hour, the lineautomation efficiency is greater and consequently the investment paybacktime is lower.

It will be understood by one having ordinary skill in the art thatconstruction of the described device and other components is not limitedto any specific material. Other exemplary embodiments of the devicedisclosed herein may be formed from a wide variety of materials, unlessdescribed otherwise herein.

For purposes of this disclosure, the term “coupled” (in all of itsforms, couple, coupling, coupled, etc.) generally means the joining oftwo components (electrical or mechanical) directly or indirectly to oneanother. Such joining may be stationary in nature or movable in nature.Such joining may be achieved with the two components (electrical ormechanical) and any additional intermediate members being integrallyformed as a single unitary body with one another or with the twocomponents. Such joining may be permanent in nature or may be removableor releasable in nature unless otherwise stated.

It is also important to note that the construction and arrangement ofthe elements of the device as shown in the exemplary embodiments isillustrative only. Although only a few embodiments of the presentinnovations have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited. For example,elements shown as integrally formed may be constructed of multiple partsor elements shown as multiple parts may be integrally formed, theoperation of the interfaces may be reversed or otherwise varied, thelength or width of the structures and/or members or connector or otherelements of the system may be varied, the nature or number of adjustmentpositions provided between the elements may be varied. It should benoted that the elements and/or assemblies of the system may beconstructed from any of a wide variety of materials that providesufficient strength or durability, in any of a wide variety of colors,textures, and combinations. Accordingly, all such modifications areintended to be included within the scope of the present innovations.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions, and arrangement of the desired andother exemplary embodiments without departing from the spirit of thepresent innovations.

It will be understood that any described processes or steps withindescribed processes may be combined with other disclosed processes orsteps to form structures within the scope of the present device. Theexemplary structures and processes disclosed herein are for illustrativepurposes and are not to be construed as limiting.

It is also to be understood that variations and modifications can bemade on the aforementioned structures and methods without departing fromthe concepts of the present device, and further it is to be understoodthat such concepts are intended to be covered by the following claimsunless these claims by their language expressly state otherwise.

The above description is considered that of the illustrated embodimentsonly. Modifications of the device will occur to those skilled in the artand to those who make or use the device. Therefore, it is understoodthat the embodiments shown in the drawings and described above is merelyfor illustrative purposes and not intended to limit the scope of thedevice, which is defined by the following claims as interpretedaccording to the principles of patent law, including the Doctrine ofEquivalents.

Listing of Non-Limiting Embodiments

Embodiment A is an induction cooking heater comprising an inductorhaving a number of magnetic field concentration bars located beneath theinductor wherein the inductor having the magnetic field concentrationbars is supported by a polymeric frame, wherein the polymeric framecomprises a first support element on which the inductor is wound and asecond support element that supports the magnetic field concentrationbars, wherein the first support element and the second support elementare assembled together through a central ring-shaped zone having a snapengagement, wherein the inductor is wound on an upper surface of thefirst support element opposite to the second support element.

The device of Embodiment A wherein the dimension of the second supportelement is lower than the dimension of the first support element.

The device of Embodiment A or Embodiment A with one or more of theintervening features wherein the second support element presents aplurality of seats for the magnetic field concentration bars, each seathaving a radial end far from the central zone open so that the seat maycontain the magnetic field concentration bars which are longer than theseats.

The device of Embodiment A or Embodiment A with one or more of theintervening features wherein an intermediate zone of the second supportelement presents a seat for a group of curved field concentration bars.

The device of Embodiment A or Embodiment A with one or more of theintervening features wherein the group of curved field concentrationbars present a plurality of flat ferrite elements having a circularsector shape.

The device of Embodiment A or Embodiment A with one or more of theintervening features wherein the first element presents a plurality ofarms stemming out from a central zone that are joined at an intermediatering.

The device of Embodiment A of Embodiment A with one or more of theintervening features wherein the intermediate ring divides the firstsupport element into two zones, a central zone with a number of firstradial arms and a second zone with a number of cantilevered secondradial arms.

The device of Embodiment A or Embodiment A with one or more of theintervening features wherein the number of first arms are identical tothe number of second arms and the first arms and the second arms areangularly shifted relative to each other.

The device of Embodiment A or Embodiment A with one or more of theintervening features wherein the number of first arms is lower than thenumber of the second arms.

The device of Embodiment A or Embodiment A with one or more of theintervening features wherein the first support element comprises a firstpolymeric material and the second support element comprises a differentsecond polymeric material.

Embodiment B is an induction cooking heater comprising an inductorhaving a number of magnetic field concentration bars located beneath theinductor wherein the inductor having the magnetic field concentrationbars is supported by a polymeric frame, wherein the polymeric framecomprises a first support element on which the inductor is wound and asecond support element that supports the magnetic field concentrationbars, wherein the first support element and the second support elementare assembled together through an annular zone having a snap engagement,wherein the inductor is wound on an upper surface of the first supportelement opposite to the second support element, wherein the firstelement presents a plurality of arms stemming out from a central zonethat are joined at an intermediate ring.

The device of Embodiment B wherein the second support element presents aplurality of seats for the magnetic field concentration bars, each seathaving a radial end far from the central zone open so that the seat maycontain the magnetic field concentration bars which are longer than theseats.

The device of Embodiment B or Embodiment B with one or more of theintervening features wherein an intermediate zone of the second supportelement presents a seat for a group of curved field concentration bars.

The device of Embodiment B or Embodiment B with one or more of theintervening features wherein the group of curved field concentrationbars present a plurality of flat ferrite elements having a circularsector shape.

The device of Embodiment B or Embodiment B with one or more of theintervening features wherein the intermediate ring divides the firstsupport element into two zones, a central zone with a number of firstradial arms and a second zone with a number of cantilevered secondradial arms.

The device of Embodiment B or Embodiment B with one or more of theintervening features wherein the number of first arms are identical tothe number of second arms and the first arms and the second arms areangularly shifted relative to each other.

The device of Embodiment B or Embodiment B with one or more of theintervening features wherein the dimension of the second support elementis lower than the dimension of the first support element.

Embodiment C is a method for producing an induction cooking heatercomprising at least one inductor and a group of magnetic fieldconcentration bars located beneath the inductor, the inductor and thegroup of magnetic field concentration bars are supported by a polymericframe comprising: winding a wire on an upper surface of a first supportelement opposite to the field concentration bars; inserting saidmagnetic field concentration bars on a second support element; andassembling together the first support element and the second supportelement.

The method of Embodiment C wherein the first support element and thesecond support element are assembled by a snap-engagement in a centralzone thereof.

The method of Embodiment C or Embodiment C with one or more of theintervening features wherein the first element presents a plurality ofarms stemming out from a central zone that are joined at an intermediatering and the intermediate ring divides the first support element intotwo zones, a central zone with a number of first radial arms and asecond zone with a number of cantilevered second radial arms.

What is claimed is:
 1. A method for producing an induction-cookingheater comprising at least one inductor and a group of magnetic fieldconcentration bars located beneath the inductor, the inductor and thegroup of magnetic field concentration bars being supported by apolymeric frame comprising: winding a wire on an upper surface of afirst support element opposite to the group of magnetic fieldconcentration bars; inserting the group of magnetic field concentrationbars on a second support element; and assembling together the firstsupport element and the second support element.
 2. The method accordingto claim 1, wherein the first support element and the second supportelement are assembled by a snap-engagement in a central zone thereof. 3.The method according to claim 1, wherein the first support elementpresents a plurality of arms stemming out from a central zone that arejoined at an intermediate ring and the intermediate ring divides thefirst support element into two zones, a central zone with a number offirst radial arms and a second zone with a number of cantilevered secondradial arms.
 4. The method according to claim 1, wherein a dimension ofthe second support element is less than the dimension of the firstsupport element.
 5. The method according to claim 2, wherein the secondsupport element presents a plurality of seats for the group of magneticfield concentration bars, each seat having a radial end distal from thecentral zone open so that the seat may contain the group of magneticfield concentration bars that are longer than the plurality of seats. 6.The method according to claim 3, wherein an intermediate zone of thesecond support element comprises a seat for a group of curved fieldconcentration bars, wherein the intermediate zone is within the centralzone.
 7. The method according to claim 6, wherein the group of curvedfield concentration bars comprise a plurality of flat ferrite elementshaving a circular sector shape.
 8. The method according to claim 3,wherein the number of first radial arms are identical to the number ofsecond radial arms and the first radial arms and the second radial armsare angularly shifted relative to each other.
 9. The method according toclaim 3, wherein the number of first radial arms is lower than thenumber of the second radial arms.
 10. A method for producing aninduction cooking heater comprising steps of: disposing a winding on anupper surface of a first support element, wherein the winding defines aninductor; disposing a group of magnetic field concentration bars on asecond support element, wherein the second support element includes aplurality of seats that respectively receive the group of magnetic fieldconcentration bars; and attaching the first support element with thesecond support element, wherein the group of magnetic fieldconcentration bars are located beneath the inductor.
 11. The methodaccording to claim 10, wherein the first support element presents aplurality of arms stemming out from a central ring-shaped zone that arejoined at an intermediate ring.
 12. The method according to claim 10,wherein an intermediate zone of the second support element comprises aseat for a group of curved field concentration bars, wherein theintermediate zone is within a central ring-shaped zone.
 13. The methodaccording to claim 12, wherein the group of curved field concentrationbars comprise a plurality of flat ferrite elements having a circularsector shape.
 14. A method for forming an induction cooking heatercomprising steps of: winding an inductor on an upper surface of a firstsupport element; disposing a plurality of magnetic field concentrationbars on a second support element; snapping together the first and secondsupport elements together through a central ring-shaped zone thatdefines a snapping engagement mechanism, wherein the plurality ofmagnetic field concentration bars are positioned beneath the inductor.15. The method according to claim 14, wherein the first and secondsupport elements cooperate to define a polymeric frame that receives theinductor and the plurality of magnetic field concentration bars.
 16. Themethod according to claim 14, wherein the first support element presentsa plurality of arms stemming out from the central ring-shaped zone thatare joined at an intermediate ring.
 17. The method according to claim16, wherein the intermediate ring divides the first support element intotwo zones, a central zone with a number of first radial arms and asecond zone with a number of cantilevered second radial arms.
 18. Themethod according to claim 14, wherein the step of disposing theplurality of magnetic field concentration bars in the second supportelement includes placing each within a respective magnetic fieldconcentration bar seat of a plurality of seats, wherein a portion of theplurality of seats includes an open radial end through which a portionof a respective magnetic field concentration bar extends.
 19. The methodaccording to claim 17, wherein the number of first radial arms areidentical to the number of second radial arms and the first radial armsand the second radial arms are angularly shifted relative to each other.20. The method according to claim 17, wherein the number of first radialarms is lower than the number of the second radial arms.